A multiscale study of dynamic gap junctions in myocyte-fibroblast interactions

 描述（由申请人提供）：成人心脏由致密的心肌细胞网络组成，周围环绕着非心肌细胞，其中最丰富的是心脏成纤维细胞。几种心脏疾病，如心肌梗死或扩张型心肌病，与成纤维细胞密度增加（纤维化）有关。已知成纤维细胞发挥 在心脏电和机械功能障碍的发展中起重要作用，但确切的机制知之甚少。一种新的机制表明，成纤维细胞通过间隙连接通道（GJC）与心肌细胞直接电相互作用促进心肌细胞发生。最近的体外研究表明，成纤维细胞可以诱导自发性电活动，改变传导速度，并通过GJC直接电耦合减少心肌细胞的动作电位时程。GJC是细胞间通道，为相邻细胞之间的通信提供直接途径。在心脏中，三种主要的连接蛋白（Cx）亚型Cx40、Cx43和Cx45以细胞类型特异性组合形成GJC。因为每个Cx的特征在于独特的动态特性（即，电压依赖性电导曲线），我假设成纤维细胞的电生理贡献将随肌细胞-成纤维细胞GJC的特定组成而变化。 理解这种电生理学贡献及其作为心脏组织类型的函数的变化，在增强的致炎状态伴随有增加的纤维化的疾病状态的背景下尤其重要。为了研究动态GJC特性在肌细胞-成纤维细胞相互作用中的作用，拟议的研究将使用多尺度实验和计算建模方法。首先，将开发肌细胞成纤维细胞GJC的动态特性的数学模型。然后，使用动态钳技术和计算机模拟，这些模型将被用来研究动态GJC表型对成纤维细胞对心肌细胞动作电位（AP）持续时间和形态的电生理贡献的影响。AP持续时间和形态的改变是心律失常发生的关键因素。此外，拟议的研究将使用一种新的方法来量化心肌组织中肌细胞和成纤维细胞之间的细胞间GJC通讯。这将是理解整个心脏中肌细胞-成纤维细胞相互作用的重要一步。最后，动态钳研究和细胞间通讯研究的结果将被纳入一个详细的二维计算模型的正常和心力衰竭组织与斑片状纤维化。这将允许动态GJC如何修改成纤维细胞介导的心脏纤维化过程中的传导速度的变化和脆弱性折返的调查。这种多尺度的计算和实验研究的肌细胞成纤维细胞的相互作用将提供机制的洞察过程中发挥关键作用，在心脏纤维化的心肌细胞电生理学的修改。

 DESCRIPTION (provided by applicant): The adult heart is composed of a dense network of cardiomyocytes surrounded by non-myocyte cells, the most abundant of which are cardiac fibroblasts. Several cardiac diseases, such as myocardial infarction or dilated cardiomyopathy, are associated with an increased density of fibroblasts (fibrosis). Fibroblasts are known to play a significant role in the development of electric and mechanical dysfunction of the heart, however the exact mechanisms are poorly understood. One emerging mechanism suggests that fibroblasts promote arrhythmogenesis through direct electrical interactions with cardiomyocytes via gap junctional channels (GJCs). Recent in vitro studies have demonstrated that fibroblasts can induce spontaneous electrical activity, modify conduction velocity, and reduce action potential duration of cardiomyocytes through direct electrical coupling via GJCs. GJCs are intercellular channels that provide a direct pathway for communication between neighboring cells. In the heart, three major connexin (Cx) isoforms, Cx40, Cx43 and Cx45 form GJCs in cell-type-specific combinations. Because each Cx is characterized by unique dynamic properties (i.e., voltage-dependent conductance profile), I hypothesize that the electrophysiological contributions of fibroblasts will vary with the specific composition of the myocyte-fibroblast GJC. Understanding such electrophysiological contributions, and their variation as a function of cardiac tissue type, is especially important in the context of the enhanced arrhythmogenic state accompanying diseased states with increased fibrosis. To investigate the role of dynamic GJC properties in myocyte-fibroblast interactions, the proposed study will use a multi-scale experimental and computational modeling approach. First, a mathematical model of the dynamic properties of the myocyte-fibroblast GJCs will be developed. Then, using the dynamic-clamp technique and computer simulations, these models will be used to investigate the effects of the dynamic GJC phenotype on the electrophysiological contribution of fibroblasts on the cardiomyocyte action potential (AP) duration and morphology. Changes in AP duration and morphology are key factors in the development of cardiac arrhythmia. Moreover, the proposed study will use a new approach to quantify intercellular GJC communication between myocytes and fibroblast in cardiac tissue. This will be important step towards under- standing the implications of myocyte-fibroblast interactions in the whole heart. Finally, the findings of the dynamic clamp studies and the intercellular communication studies will be incorporated into a detailed two-dimensional computational model of normal and heart failure tissue with patchy fibrosis. This will allow for an investigation of how dynamic GJCs modify fibroblast-mediated changes in conduction velocity and vulnerability to reentry during cardiac fibrosis. Such a multi-scale computational and experimental investigation of myocyte-fibroblast interactions will provide mechanistic insight into which processes play a key role in modifying the cardiomyocyte electrophysiology during cardiac fibrosis.